In this article, ICN’s climate correspondent Isla Graves explores the underappreciated role of blue carbon ecosystems in the fight against climate change, why they are often overlooked, and the emerging array of initiatives to ensure their protection and revival.

Mangroves are back at a formerly degraded area in Yucatan, Ciénaga del Progures. Photo by Yoly Gutierrez/CIFOR (cifor.org / forestsnews.cifor.org)

When you hear the phrase ‘carbon sinks’, which ecosystems come to mind?

Probably tropical rainforests, maybe the soil and perhaps the permafrost layer in the tundra.

You may not think of mangrove swamps, seagrass meadows and tidal marshes.

These habitats fall under the umbrella term ‘blue carbon ecosystems’. ‘Blue carbon’ refers to organic carbon, mainly from decaying plants and animals, which is captured and stored by the ocean and coastal ecosystems.

These ‘blue carbon ecosystems’ are, however, some of the most important carbon sinks in the world. Despite only covering 1% of the world’s oceans, they are responsible for around half of the carbon dioxide absorbed by oceans. One hectare of seagrass can soak up as much carbon dioxide each year as fifteen hectares of rainforest, according to UNESCO.[1]

Blue carbon ecosystems are a relatively new field of study. Only over the last couple of decades have scientists confirmed that “seagrass meadows, tidal marshes, and mangroves … are some of the most intensive carbon sinks in the biosphere”.[2] In March 2021, UNESCO published its first report into these blue carbon ecosystems. In total, around 33 billion tonnes of carbon dioxide (about three-quarters of the world’s emissions in 2019) are locked away in blue-carbon sinks globally.

Seagrass meadows, tidal marshes and mangrove swamps therefore form a crucial border around coastlines globally. They play important ecological roles in nutrient and carbon cycling, are habitats for many marine and terrestrial species, act as shoreline protection, and sustain the livelihoods of local communities. One reason that these sinks are so effective is that submerged forests have a much higher density than those on land. They can also trap floating debris, which settles as sediment on the sea floor and increases the amount of carbon stored.

One hectare of seagrass can soak up as much carbon dioxide each year as fifteen hectares of rainforest, according to UNESCO

These blue carbon ecosystems sequester significant amounts of carbon from the atmosphere, and therefore have a vital role to play in mitigation against climate change. Blue carbon systems are not as exposed to wildfires as inland forests, which are releasing large amounts of carbon as the changing climate makes fires more destructive. Moreover, not only are carbon stocks released into the atmosphere as forests burn, but the fires also hinder forests’ future ability to capture carbon. This is because repeated fires favour slow-growing tree species, which are better able to survive burning, and these species are less effective at absorbing carbon than faster growing trees.[3] Nonetheless, while blue carbon ecosystems do not suffer from this problem, they are vulnerable to other forms of climate-related degradation and human-induced destruction. This means their protection is a key issue in the fight against climate change.

We might ask why these blue carbon ecosystems have such a low profile despite their critical importance. Sadly, they have often been overlooked in favour of more ‘exciting’ ecosystems such as coral reefs, which attract research and funding and therefore are much more likely to be protected marine areas. Mangroves, tidal marshes and seagrasses are also more vulnerable to degradation due to land use conversion as well as eutrophication, overfishing and climate change. As these ecosystems store so much carbon, they have the potential to become significant sources of CO2 emissions if they are destroyed.

By conserving blue carbon ecosystems, the large carbon stocks that have accumulated over millennia can be protected. As they are restored, they can regain their function as carbon sinks”.[4] This approach and indeed the definition of ‘blue carbon ecosystems’ was first outlined in a 2009 UNEP report “Blue Carbon. The role of healthy oceans in binding carbon”. Further evidence for the resilience of these ecosystems is the restoration of mangrove forests in Vietnam after damage sustained during the Vietnam War, according to a 2014 report by the International Society for Mangrove Ecosystems. More than half of the mangrove forests in the Mekong Delta were destroyed by napalm and herbicides however an intense reforesting effort restored the mangroves within two decades.

Protection of mangrove forests, seagrass meadows and tidal marshes is beginning to emerge as a key international priority. 2021-2030 is not only the United Nations Decade of Ocean Science for Sustainable Development but also the United Nations Decade of Ecosystem Restoration. Investment in the maintenance and protection of these ecosystems can “offer significant opportunities to mitigate climate change, meet the goals of the Paris Agreement under the United Nations Framework Convention on Climate Change by including these assets in Nationally Determined Contributions, and finance conservation, at least in part, through the resulting carbon credits”.[5]

Moreover, a growing source of potential funding for the protection of these ecosystems is from companies seeking to remove carbon from the atmosphere, and particularly those who want to work with natural processes instead of human technologies such as direct air capture. Many companies are now seeking to become less carbon-intensive, or more ambitiously, carbon-neutral through carbon offsetting (although this practice is controversial). For example, in 2018 Apple collaborated with the charity Conservation International to protect 11,000 hectares of mangroves along the Colombian coast, estimated to absorb about one million tonnes of carbon.[6]

There are other causes for hope. In advance of the COP15 Biodiversity Conference in October and the COP26 climate change summit in November, the Environmental Justice Foundation (EJF) has written an open letter calling for blue carbon ecosystems to receive greater protection. The demands call on climate representatives to:

  • Include specific blue carbon protection and restoration targets in each country’s Nationally Determined Contributions.
  • Designate 30% of the ocean as ecologically protected by 2030 and commit to the 30×30 protection plan.
  • Agree an international moratorium on deep sea mining to protect the deep sea from irreversible harm.

More than 3000 scientists, policymakers, and public figures as well as 66 NGOs have signed the letter and hope it will provoke discussion at COP26 and the COP15 Biodiversity Conference. EJF Executive Director Steve Trent commented: “Our political leaders must recognise the urgency of the climate crisis and take truly bold, transformative action to reach a global zero carbon economy.”[7]

Finally, alongside policymakers, partnerships are being forged between businesses and NGOs to protect these ecosystems, for example between Carlsberg and WWF. Purchases of special edition packs of Carlsberg will contribute a 50p donation towards the WWF’s efforts to restore seagrass habitats. The aim is to restore 20 hectares of seagrass around UK shores by 2026. A donation will also be made for each pint of Carlsberg bought when pubs reopen (at selected partner pubs). Carlsberg UK’s Director of Marketing Emma Sherwood-Smith remarked, “Our campaign with WWF helps to highlight the small changes needed to make a big difference.”[8]

This seemingly unlikely partnership hints at the way forward: cooperation between a wide range of stakeholders including governments, businesses and NGOs to achieve a common goal. “We are in the midst of a climate and nature crisis, and WWF can’t achieve our mission of a sustainable future on our own” observed WWF executive director of advocacy and campaigns, Kate Norgrove. “We need to work with brands that care about our planet …  to inspire as many people as possible in the fight for our world.”


[1] UNESCO https://whc.unesco.org/en/blue-carbon-report/

[2] Ibid.

[3] Nature Ecology Evolution: https://doi.org/10.1038/s41559-021-01401-7

[4] UNESCO

[5] UNESCO

[6] The Economist: https://www.economist.com/science-and-technology/2021/03/06/seagrasses-and-mangroves-can-suck-carbon-from-the-air

[7] EJF: https://ejfoundation.org/news-media/open-letter-to-world-leaders-put-marine-ecosystems-at-the-heart-of-climate-policy

[8] Edie: https://www.edie.net/news/9/Carlsberg-and-WWF-launch-seagrass-restoration-project/